Java 代码实例解析设计模式之监听者模式

所谓监听者模式，我理解的是构建一个容器存放所有被监听的线程或对象，监听每个线程或对象发生的变化，若某个线程或对象触发指定规则，那么则对所有被监听的线程或对象根据业务需要做处理

代码展示

Main：测试类

ObServer：每个被监听的对象实现该接口，重写该方法，完成自己的业务

 public interface ObServer { /** * 当某一个被监控的对象发生变化时 * 所有实现该方法处理方法 */ void exceptionHandler(); }

Subject：监听者容器

 public interface Subject { /** * 添加被观察对象 */ void add(ObServer obServer); /** * 通知所有被观察者完成自己的 exceptionHandler 方法 */ void notifyAllSubject(); }

SubjectHandler：监听者容器的实现类

 public class SubjectHandler implements Subject { /** * 存放被监听对象 */ private static final List SUBJECTS = Collections.synchronizedList(new LinkedList<>()); @Override public void add(ObServer subject) { SUBJECTS.add(subject); } @Override public void notifyAllSubject() { SUBJECTS.forEach(ObServer::exceptionHandler); } }

Thread1、Thread2 测试对象

模拟两个线程对数据库操作，若Threa1执行时出异常了，那么终止所有线程并对其回滚。

Threa1:

 public class Thread1 implements ObServer, Runnable { @SneakyThrows @Override public void run() { System.out.println("thread1 run"); Thread.sleep(1000); System.out.println("t1 end"); } @SneakyThrows @Override public void exceptionHandler() { System.out.println("thread1 rollback....."); } }

Thread2:

 public class Thread2 implements ObServer, Runnable { private static Thread CURRENT_THREAD; private static volatile boolean FLAG = false; @SneakyThrows @Override public void run() { CURRENT_THREAD = Thread.currentThread(); System.out.println("thread2 running"); int count = 0; while (!FLAG) { System.out.println(count); count++; } System.out.println("thread2 end"); } @SneakyThrows @Override public void exceptionHandler() { FLAG = true; CURRENT_THREAD.interrupt(); System.out.println("thread2 rollback....."); } }

测试Demo

 public static void main(String[] args) throws InterruptedException { // 创建监听容器 Subject subject = new SubjectHandler(); Thread1 thread1 = new Thread1(); Thread2 thread2 = new Thread2(); subject.add(thread1); subject.add(thread2); CompletableFuture.supplyAsync(() -> { new Thread(thread1).start(); try { Thread.sleep(10); int a = 1 / 0; // 模拟线程1报错 } catch (InterruptedException e) { e.printStackTrace(); } return true; }).exceptionally((error) -> { subject.notifyAllSubject(); return false; }); CompletableFuture.supplyAsync(() -> { new Thread(thread2).start(); return true; }).exceptionally((error) -> { subject.notifyAllSubject(); return false; }); // main thread await Thread.sleep(60 * 1000); }

测试结果